The present invention relates to a material testing device for testing mechanical properties of a very fine material in a thin film form by applying a stress on the material, a material testing apparatus for carrying out the test and a method of testing the material.
Intensive researches are carried out on the micro-machining technology of a semiconductor, or the MEMS (Micro-Electro-Mechanical Systems) in which a mechanical structure having a size of several tens through one hundred .mu.m is prepared by using, for example, photolithography, etching, thin film forming technology or the like and the mechanical structure is applied to a sensor, an optical element or a mechanical device, or on a micromachine. With respect to such a new device, a single crystal of silicon or an oxide film, a nitride film or the like formed on the surface of the single crystal of silicon is used in place of a conventional metal material such as steel or the like.
The mechanical properties such as elastic modulus, yield stress or the like of these materials are important factors controlling the function of the device of the MEMS. Meanwhile, it is known that the mechanical properties of these thin films are significantly varied by the manufacturing processes of these and therefore, and the importance of the method of measuring and evaluating these materials has been emphasized.
As conventionally proposed methods of measuring and evaluating these materials, there are methods where a diaphragm is prepared by a thin film and an amount of bulging of the diaphragm when an air pressure is applied thereon, is measured, a method using a micro hardness tester in which an indenter is pushed into a test piece, a method in which a very small tensile test piece is prepared and the test piece is pulled by attaching the test piece to a tensile tester or the like.
However, according to the conventional method of measuring the amount of bulging of a diaphragm, although the elastic modulus can be measured, the yield stress cannot be measured. Further, although the method of using a micro hardness tester for pushing in an indenter into a test piece, is simple for evaluating the yield stress of a ductile metal, the method is difficult to apply to a brittle material such as silicon and compounds of silicon.
Although the method using a tensile tester is one of the most preferable testing methods in evaluating the mechanical properties, when a very small test piece that is easy to destruct, is chucked or adhered to a tensile tester, the brittle test piece may be destructed, or a bending stress may be superposed thereon because the axis of the test piece is not in alignment with the axis of tension, or the like. Further, the measurement accuracy of strain may be low since the displacement in elongating the test piece having a short gage length is small.